Method for d2d signal transmission in wireless communication system, and terminal using same

ABSTRACT

Provided is a method for device-to-device (D2D) signal transmission performed by a terminal in a wireless communication system, and a terminal device using the method. The method is characterized by: receiving measurement carrier (MEA_CARRIER) indication information which indicates a single downlink carrier to be used in downlink measurement and synchronization for D2D operation; and using, for the downlink measurement and synchronization for D2D operation, the single downlink carrier indicated by the measurement carrier (MEA_CARRIER) indication information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2016/000020, filed on Jan. 4, 2016,which claims the benefit of U.S. Provisional Applications No. 62/099,213filed on Jan. 2, 2015, No. 62/103,503 filed on Jan. 14, 2015, No.62/151,415 filed on Apr. 23, 2015, and No. 62/190,754 filed on Jul. 10,2015, the contents of which are all hereby incorporated by referenceherein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a method for transmitting a D2D (device-to-device)signal by a user device in a wireless communication system and the userdevice using the method.

Related Art

In International Telecommunication Union Radio communication sector(ITU-R), a standardization task for International MobileTelecommunication (IMT)-Advanced, that is, the next-generation mobilecommunication system since the third generation, is in progress.IMT-Advanced sets its goal to support Internet Protocol (IP)-basedmultimedia services at a data transfer rate of 1 Gbps in the stop andslow-speed moving state and of 100 Mbps in the fast-speed moving state.

For example, 3^(rd) Generation Partnership Project (3GPP) is a systemstandard to satisfy the requirements of IMT-Advanced and is preparingfor LTE-Advanced improved from Long Term Evolution (LTE) based onOrthogonal Frequency Division Multiple Access (OFDMA)/SingleCarrier-Frequency Division Multiple Access (SC-FDMA) transmissionschemes. LTE-Advanced is one of strong candidates for IMT-Advanced.

There is a growing interest in a Device-to-Device (D22) technology inwhich devices perform direct communication. In particular, D2D has beenin the spotlight as a communication technology for a public safetynetwork. A commercial communication network is rapidly changing to LTE,but the current public safety network is basically based on the 2Gtechnology in terms of a collision problem with existing communicationstandards and a cost. Such a technology gap and a need for improvedservices are leading to efforts to improve the public safety network.

The public safety network has higher service requirements (reliabilityand security) than the commercial communication network. In particular,if coverage of cellular communication is not affected or available, thepublic safety network also requires direct communication betweendevices, that is, D2D operation.

D2D operation may have various advantages in that it is communicationbetween devices in proximity. For example, D2D UE has a high transferrate and a low delay and may perform data communication. Furthermore, inD2D operation, traffic concentrated on a base station can bedistributed. If D2D UE plays the role of a relay, it may also play therole of extending coverage of a base station.

Meanwhile, a UE may have a radio resource control (RRC) connection witha network through a specific carrier wave. In this case, the specificcarrier may be referred to as a primary carrier. Conventionally, the UEis assumed to perform the D2D operation only using the primary carrierwave. However, currently, it is also considered to perform the D2Doperation using a carrier wave other than the primary carrier wave, andthe serving cell for the UE is not present using the other carrier wave.In this case, it is not clear how to perform downlink measurement orsynchronization necessary for the UE to perform the D2D operation, inparticular, the D2D signal transmission.

SUMMARY OF THE INVENTION

The present invention is to provide a method for transmitting a D2D(device-to-device) signal by a user device in a wireless communicationsystem and the user device using the method.

In one aspect, provided is a method for transmitting a device-to-device(D2D) signal by a user device in a wireless communication system. Themethod includes receiving a measurement carrier (MEA_CARRIER) indicationinformation indicating one downlink carrier used for downlinkmeasurement and synchronization for D2D operation using one downlinkcarrier indicated by the measurement carrier (MEA_CARRIER) indicationinformation to perform downlink measurement and synchronization for theD2D operation.

The D2D operation may be a transmission of a D2D discovery signal.

The D2D discovery signal may be transmitted via a non-primary carrierrather than a primary carrier.

If there is an active serving cell for the user device, the serving cellusing a non-primary carrier rather than a primary carrier fortransmission of the D2D discovery signal, the activated serving cell maybe used to perform downlink measurement and synchronization for the D2Doperation.

If there is not an active serving cell for the user device, the servingcell using a non-primary carrier rather than a primary carrier fortransmission of the D2D discovery signal, said one downlink carrierindicated by the measurement carrier (MEA_CARRIER) indicationinformation may be used to perform downlink measurement andsynchronization for the D2D operation.

The one downlink carrier may be a carrier linked to the non-primarycarrier rather than the primary carrier via system information.

The one downlink carrier may be a carrier not linked to the non-primarycarrier rather than the primary carrier via system information.

In another aspect, provided is a user equipment. The user equipmentincludes an RF (Radio Frequency) unit for transmitting and receiving aradio signal and a processor coupled to the RF unit. The processor isconfigured to receive a measurement carrier (MEA_CARRIER) indicationinformation indicating one downlink carrier used for downlinkmeasurement and synchronization for D2D operation and to use said onedownlink carrier indicated by the measurement carrier (MEA_CARRIER)indication information to perform downlink measurement andsynchronization for the D2D operation.

The UE may transmit the D2D signal on a carrier other than the primarycarrier having the RRC connection with the network. Downlink measurementand synchronization may be required to transmit the D2D signal. In thisconnection, in one example, the UE may not have hardware to measure theother carrier. In this case, according to the prior art, it is unclearhow to perform downlink measurement and synchronization, which may causeproblems in D2D signal transmission. The present invention can solve theproblem by signaling, by the serving cell, the downlink carrier used fordownlink measurement and synchronization for D2D signal transmission tothe UE in the above case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane.

FIG. 3 is a diagram showing a wireless protocol architecture for acontrol plane.

FIG. 4 shows a basic structure for ProSe.

FIG. 5 shows the deployment examples of types of UE performing ProSedirect communication and cell coverage.

FIG. 6 is an embodiment of a ProSe discovery process.

FIG. 7 is another embodiment of a ProSe discovery process.

FIG. 8 shows an example of the UE providing the relay functionality.

FIG. 9 shows DL CARRIER#X, UL CARRIER#X, and CARRIER#Y set for DRUE#N.

FIG. 10 illustrates a specific method using the example#4 above.

FIG. 11 illustrates a method of transmitting a D2D discovery signal bythe user device according to an embodiment of the present invention.

FIG. 12 illustrates a situation in which the user device performs a D2Doperation.

FIG. 13 is a method for performing the D2D operation by the user devicewhen Rule#A-2 is applied.

FIG. 14 illustrates another situation in which the user device performsD2D operation.

FIG. 15 is a block diagram illustrating the user device in which anembodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system.

The wireless communication system may be referred to as an Evolved-UMTSTerrestrial Radio Access Network (E-UTRAN) or a Long Term Evolution(LTE)/LTE-A system, for example.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane. FIG. 3 is a diagram showing a wireless protocol architecture fora control plane. The user plane is a protocol stack for user datatransmission. The control plane is a protocol stack for control signaltransmission.

Referring to FIGS. 2 and 3, a PHY layer provides an upper layer with aninformation transfer service through a physical channel The PHY layer isconnected to a medium access control (MAC) layer which is an upper layerof the PHY layer through a transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transferred through a radio interface.

Data is moved between different PHY layers, that is, the PHY layers of atransmitter and a receiver, through a physical channel. The physicalchannel may be modulated according to an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, and use the time and frequency as radioresources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing and demultiplexing to atransport block that is provided through a physical channel on thetransport channel of a MAC Service Data Unit (SDU) that belongs to alogical channel The MAC layer provides service to a Radio Link Control(RLC) layer through the logical channel

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three types of operation mode: Transparent Mode (TM),Unacknowledged Mode (UM), and Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The RRC layer is defined only on the control plane. The RRC layer isrelated to the configuration, reconfiguration, and release of radiobearers, and is responsible for control of logical channels, transportchannels, and PHY channels. An RB means a logical route that is providedby the first layer (PHY layer) and the second layers (MAC layer, the RLClayer, and the PDCP layer) in order to transfer data between UE and anetwork.

The function of a Packet Data Convergence Protocol (PDCP) layer on theuser plane includes the transfer of user data and header compression andciphering. The function of the PDCP layer on the user plane furtherincludes the transfer and encryption/integrity protection of controlplane data.

What an RB is configured means a process of defining the characteristicsof a wireless protocol layer and channels in order to provide specificservice and configuring each detailed parameter and operating method. AnRB can be divided into two types of a Signaling RB (SRB) and a Data RB(DRB). The SRB is used as a passage through which an RRC message istransmitted on the control plane, and the DRB is used as a passagethrough which user data is transmitted on the user plane.

If RRC connection is established between the RRC layer of UE and the RRClayer of an E-UTRAN, the UE is in the RRC connected state. If not, theUE is in the RRC idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through the downlink SCH, or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or control messages are transmitted.

Logical channels that are placed over the transport channel and that aremapped to the transport channel include a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), and a multicast trafficchannel (MTCH).

The physical channel includes several OFDM symbols in the time domainand several subcarriers in the frequency domain. One subframe includes aplurality of OFDM symbols in the time domain. An RB is a resourcesallocation unit, and includes a plurality of 01-DM symbols and aplurality of subcarriers. Furthermore, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) ofthe corresponding subframe for a physical downlink control channel(PDCCH), that is, an L1/L2 control channel. A Transmission Time Interval(TTI) is a unit time for subframe transmission.

The RRC state means whether or not the RRC layer of UE is logicallyconnected to the RRC layer of the E-UTRAN. A case where the RRC layer ofUE is logically connected to the RRC layer of the E-UTRAN is referred toas an RRC connected state. A case where the RRC layer of UE is notlogically connected to the RRC layer of the E-UTRAN is referred to as anRRC idle state. The E-UTRAN may check the existence of corresponding UEin the RRC connected state in each cell because the UE has RRCconnection, so the UE may be effectively controlled. In contrast, theE-UTRAN is unable to check UE in the RRC idle state, and a Core Network(CN) manages UE in the RRC idle state in each tracking area, that is,the unit of an area greater than a cell. That is, the existence ornon-existence of UE in the RRC idle state is checked only for each largearea. Accordingly, the UE needs to shift to the RRC connected state inorder to be provided with common mobile communication service, such asvoice or data.

When a user first powers UE, the UE first searches for a proper cell andremains in the RRC idle state in the corresponding cell. The UE in theRRC idle state establishes RRC connection with an E-UTRAN through an RRCconnection procedure when it is necessary to set up the RRC connection,and shifts to the RRC connected state. A case where UE in the RRC idlestate needs to set up RRC connection includes several cases. Forexample, the cases may include a need to send uplink data for a reason,such as a call attempt by a user, and to send a response message as aresponse to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

In the NAS layer, in order to manage the mobility of UE, two types ofstates: EPS Mobility Management-REGISTERED (EMM-REGISTERED) andEMM-DEREGISTERED are defined. The two states are applied to UE and theMME. UE is initially in the EMM-DEREGISTERED state. In order to access anetwork, the UE performs a process of registering it with thecorresponding network through an initial attach procedure. If the attachprocedure is successfully performed, the UE and the MME become theEMM-REGISTERED state.

In order to manage signaling connection between UE and the EPC, twotypes of states: an EPS Connection Management (ECM)-IDLE state and anECM-CONNECTED state are defined. The two states are applied to UE andthe MME. When the UE in the ECM-IDLE state establishes RRC connectionwith the E-UTRAN, the UE becomes the ECM-CONNECTED state. The MME in theECM-IDLE state becomes the ECM-CONNECTED state when it establishes S1connection with the E-UTRAN. When the UE is in the ECM-IDLE state, theE-UTRAN does not have information about the context of the UE.Accordingly, the UE in the ECM-IDLE state performs procedures related toUE-based mobility, such as cell selection or cell reselection, without aneed to receive a command from a network. In contrast, when the UE is inthe ECM-CONNECTED state, the mobility of the UE is managed in responseto a command from a network. If the location of the UE in the ECM-IDLEstate is different from a location known to the network, the UE informsthe network of its corresponding location through a tracking area updateprocedure.

The D2D operation will now be described. In 3GPP LTE-A, the servicerelated to D2D operation is called proximity based service (ProSe).Hereinafter, ProSe is equivalent to D2D operation and ProSe may beinterchanged with D2D operation. ProSe will now be described.

The ProSe includes ProSe direction communication and ProSe directdiscovery. The ProSe direct communication is communication performedbetween two or more proximate UEs. The UEs may perform communication byusing a protocol of a user plane. A ProSe-enabled UE implies a UEsupporting a procedure related to a requirement of the ProSe. Unlessotherwise specified, the ProSe-enabled UE includes both of a publicsafety UE and a non-public safety UE. The public safety UE is a UEsupporting both of a function specified for a public safety and a ProSeprocedure, and the non-public safety UE is a UE supporting the ProSeprocedure and not supporting the function specified for the publicsafety.

ProSe direct discovery is a process for discovering anotherProSe-enabled UE adjacent to ProSe-enabled UE. In this case, only thecapabilities of the two types of ProSe-enabled UE are used. EPC-levelProSe discovery means a process for determining, by an EPC, whether thetwo types of ProSe-enabled UE are in proximity and notifying the twotypes of ProSe-enabled UE of the proximity

Hereinafter, for convenience, the ProSe direct communication may bereferred to as D2D communication, and the ProSe direct discovery may bereferred to as D2D discovery.

FIG. 4 shows a basic structure for ProSe.

Referring to FIG. 4, the basic structure for ProSe includes an E-UTRAN,an EPC, a plurality of types of UE including a ProSe applicationprogram, a ProSe application server (a ProSe APP server), and a ProSefunction.

The EPC represents an E-UTRAN core network configuration. The EPC mayinclude an MME, an S-GW, a P-GW, a policy and charging rules function(PCRF), a home subscriber server (HSS) and so on.

The ProSe APP server is a user of a ProSe capability for producing anapplication function. The ProSe APP server may communicate with anapplication program within UE. The application program within UE may usea ProSe capability for producing an application function.

The ProSe function may include at least one of the followings, but isnot necessarily limited thereto.

-   -   Interworking via a reference point toward the 3rd party        applications    -   Authorization and configuration of UE for discovery and direct        communication    -   Enable the functionality of EPC level ProSe discovery    -   ProSe related new subscriber data and handling of data storage,        and also handling of the ProSe identities    -   Security related functionality    -   Provide control towards the EPC for policy related functionality    -   Provide functionality for charging (via or outside of the EPC,        e.g., offline charging)

A reference point and a reference interface in the basic structure forProSe are described below.

-   -   PC1: a reference point between the ProSe application program        within the UE and the ProSe application program within the ProSe        APP server. This is used to define signaling requirements in an        application dimension.    -   PC2: a reference point between the ProSe APP server and the        ProSe function. This is used to define an interaction between        the ProSe APP server and the ProSe function. The update of        application data in the ProSe database of the ProSe function may        be an example of the interaction.    -   PC3: a reference point between the UE and the ProSe function.        This is used to define an interaction between the UE and the        ProSe function. A configuration for ProSe discovery and        communication may be an example of the interaction.    -   PC4: a reference point between the EPC and the ProSe function.        This is used to define an interaction between the EPC and the        ProSe function. The interaction may illustrate the time when a        path for 1:1 communication between types of UE is set up or the        time when ProSe service for real-time session management or        mobility management is authenticated.    -   PCS: a reference point used for using control/user plane for        discovery and communication, relay, and 1:1 communication        between types of UE.    -   PC6: a reference point for using a function, such as ProSe        discovery, between users belonging to different PLMNs.    -   SGi: this may be used to exchange application data and types of        application dimension control information.

The D2D operation may be supported both when UE is serviced within thecoverage of a network (cell) or when it is out of coverage of thenetwork.

FIG. 5 shows the deployment examples of types of UE performing ProSedirect communication and cell coverage.

Referring to FIG. 5(a), types of UE A and B may be placed outside cellcoverage. Referring to FIG. 5(b), UE A may be placed within cellcoverage, and UE B may be placed outside cell coverage. Referring toFIG. 5(c), types of UE A and B may be placed within single cellcoverage. Referring to FIG. 5(d), UE A may be placed within coverage ofa first cell, and UE B may be placed within coverage of a second cell.

ProSe direct communication may be performed between types of UE placedat various positions as in FIG. 5.

<Radio Resource Allocation for D2D Communication (ProSe DirectCommunication)>.

At least one of the following two modes may be used for resourceallocation for D2D communication.

1. Mode 1

Mode 1 is mode in which resources for ProSe direct communication arescheduled by an eNB. UE needs to be in the RRC_CONNECTED state in orderto send data in accordance with mode 1. The UE requests a transmissionresource from an eNB. The eNB performs scheduling assignment andschedules resources for sending data. The UE may send a schedulingrequest to the eNB and send a ProSe Buffer Status Report (BSR). The eNBhas data to be subjected to ProSe direct communication by the UE basedon the ProSe BSR and determines that a resource for transmission isrequired.

2. Mode 2

Mode 2 is mode in which UE directly selects a resource. UE directlyselects a resource for ProSe direct communication in a resource pool.The resource pool may be configured by a network or may have beenpreviously determined.

Meanwhile, if UE has a serving cell, that is, if the UE is in theRRC_CONNECTED state with an eNB or is placed in a specific cell in theRRC_IDLE state, the UE is considered to be placed within coverage of theeNB.

If UE is placed outside coverage, only mode 2 may be applied. If the UEis placed within the coverage, the UE may use mode 1 or mode 2 dependingon the configuration of an eNB.

If another exception condition is not present, only when an eNB performsa configuration, UE may change mode from mode 1 to mode 2 or from mode 2to mode 1.

<D2D Discovery (ProSe Direct Discovery)>

D2D discovery refers to the procedure used in a ProSe capable terminaldiscovering other ProSe capable terminals in close proximity thereto andmay be referred to as ProSe direct discovery. The information used forProSe direct discovery is hereinafter referred to as discoveryinformation.

A PC 5 interface may be used for D2D discovery. The PC 5 interfaceincludes an MAC layer, a PHY layer, and a ProSe Protocol layer, that is,a higher layer. The higher layer (the ProSe Protocol) handles thepermission of the announcement and monitoring of discovery information.The contents of the discovery information are transparent to an accessstratum (AS). The ProSe Protocol transfers only valid discoveryinformation to the AS for announcement. The MAC layer receives discoveryinformation from the higher layer (the ProSe Protocol). An IP layer isnot used to send discovery information. The MAC layer determines aresource used to announce discovery information received from the higherlayer. The MAC layer produces an MAC protocol data unit (PDU) forcarrying discovery information and sends the MAC PDU to the physicallayer. An MAC header is not added.

In order to announce discovery information, there are two types ofresource assignment.

1. Type 1

The type 1 is a method for assigning a resource for announcing discoveryinformation in a UE-not-specific manner. An eNB provides a resource poolconfiguration for discovery information announcement to types of UE. Theconfiguration may be broadcasted through the SIB. The configuration maybe provided through a UE-specific RRC message. Or the configuration maybe broadcasted through other than the RRC message in other layer or maybe provided by UE-specific signaling.

UE autonomously selects a resource from an indicated resource pool andannounces discovery information using the selected resource. The UE mayannounce the discovery information through a randomly selected resourceduring each discovery period.

2. Type 2

The type 2 is a method for assigning a resource for announcing discoveryinformation in a UE-specific manner. UE in the RRC_CONNECTED state mayrequest a resource for discovery signal announcement from an eNB throughan RRC signal. The eNB may announce a resource for discovery signalannouncement through an RRC signal. A resource for discovery signalmonitoring may be assigned within a resource pool configured for typesof UE.

An eNB 1) may announce a type 1 resource pool for discovery signalannouncement to UE in the RRC_IDLE state through the SIB. Types of UEwhose ProSe direct discovery has been permitted use the type 1 resourcepool for discovery information announcement in the RRC_IDLE state.Alternatively, the eNB 2) announces that the eNB supports ProSe directdiscovery through the SIB, but may not provide a resource for discoveryinformation announcement. In this case, UE needs to enter theRRC_CONNECTED state for discovery information announcement.

An eNB may configure that UE has to use a type 1 resource pool fordiscovery information announcement or has to use a type 2 resourcethrough an RRC signal in relation to UE in the RRC CONNECTED state.

FIG. 6 is an embodiment of a ProSe discovery process.

Referring to FIG. 6, it is assumed that UE A and UE B have ProSe-enabledapplication programs managed therein and have been configured to have a‘friend’ relation between them in the application programs, that is, arelationship in which D2D communication may be permitted between them.Hereinafter, the UE B may be represented as a ‘friend’ of the UE A. Theapplication program may be, for example, a social networking program.‘3GPP Layers’ correspond to the functions of an application program forusing ProSe discovery service, which have been defined by 3GPP.

Direct discovery between the types of UE A and B may experience thefollowing process.

1. First, the UE A performs regular application layer communication withthe APP server. The communication is based on an Application ProgramInterface (API).

2. The ProSe-enabled application program of the UE A receives a list ofapplication layer IDs having a ‘friend’ relation. In general, theapplication layer ID may have a network access ID form. For example, theapplication layer ID of the UE A may have a form, such as“adam@example.com.”

3. The UE A requests private expressions code for the user of the UE Aand private representation code for a friend of the user.

4. The 3GPP layers send a representation code request to the ProSeserver.

5. The ProSe server maps the application layer IDs, provided by anoperator or a third party APP server, to the private representationcode. For example, an application layer ID, such as adam@example.com,may be mapped to private representation code, such as“GTER543$#2FSJ67DFSF.” Such mapping may be performed based on parameters(e.g., a mapping algorithm, a key value and so on) received from the APPserver of a network.

6. The ProSe server sends the types of derived representation code tothe 3GPP layers. The 3GPP layers announce the successful reception ofthe types of representation code for the requested application layer IDto the ProSe-enabled application program. Furthermore, the 3GPP layersgenerate a mapping table between the application layer ID and the typesof representation code.

7. The ProSe-enabled application program requests the 3GPP layers tostart a discovery procedure. That is, the ProSe-enabled applicationprogram requests the 3GPP layers to start discovery when one of provided‘friends’ is placed in proximity to the UE A and direct communication ispossible. The 3GPP layers announces the private representation code(i.e., in the above example, “GTER543$#2FSJ67DFSF”, that is, the privaterepresentation code of adam@example.com) of the UE A. This ishereinafter called ‘announcement’. Mapping between the application layerID of the corresponding application program and the privaterepresentation code may be known to only ‘friends’ which have previouslyreceived such a mapping relation, and the ‘friends’ may perform suchmapping.

8. It is assumed that the UE B operates the same ProSe-enabledapplication program as the UE A and has executed the aforementioned 3 to6 steps. The 3GPP layers placed in the UE B may execute ProSe discovery.

9. When the UE B receives the aforementioned ‘announce’ from the UE A,the UE B determines whether the private representation code included inthe ‘announce’ is known to the UE B and whether the privaterepresentation code is mapped to the application layer ID. As describedthe 8 step, since the UE B has also executed the 3 to 6 steps, it isaware of the private representation code, mapping between the privaterepresentation code and the application layer ID, and correspondingapplication program of the UE A. Accordingly, the UE B may discover theUE A from the ‘announce’ of the UE A. The 3GPP layers announce thatadam@example.com has been discovered to the ProSe-enabled applicationprogram within the UE B.

In FIG. 6, the discovery procedure has been described by taking intoconsideration all of the types of UE A and B, the ProSe server, the APPserver and so on. From the viewpoint of the operation between the typesof UE A and B, the UE A sends (this process may be called announcement)a signal called announcement, and the UE B receives the announce anddiscovers the UE A. That is, from the aspect that an operation thatbelongs to operations performed by types of UE and that is directlyrelated to another UE is only step, the discovery process of FIG. 6 mayalso be called a single step discovery procedure.

FIG. 7 is another embodiment of a ProSe discovery process.

In FIG. 7, types of UE 1 to 4 are assumed to types of UE included inspecific group communication system enablers (GCSE) group. It is assumedthat the UE 1 is a discoverer and the types of UE 2, 3, and 4 arediscoveree. UE 5 is UE not related to the discovery process.

The UE 1 and the UE 2-4 may perform a next operation in the discoveryprocess.

First, the UE 1 broadcasts a target discovery request message (may behereinafter abbreviated as a discovery request message or M1) in orderto discover whether specific UE included in the GCSE group is inproximity. The target discovery request message may include the uniqueapplication program group ID or layer-2 group ID of the specific GCSEgroup. Furthermore, the target discovery request message may include theunique ID, that is, application program private ID of the UE 1. Thetarget discovery request message may be received by the types of UE 2,3, 4, and 5.

The UE 5 sends no response message. In contrast, the types of UE 2, 3,and 4 included in the GCSE group send a target discovery responsemessage (may be hereinafter abbreviated as a discovery response messageor M2) as a response to the target discovery request message. The targetdiscovery response message may include the unique application programprivate ID of UE sending the message.

An operation between types of UE in the ProSe discovery processdescribed with reference to FIG. 7 is described below. The discoverer(the UE 1) sends a target discovery request message and receives atarget discovery response message, that is, a response to the targetdiscovery request message. Furthermore, when the discoveree (e.g., theUE 2) receives the target discovery request message, it sends a targetdiscovery response message, that is, a response to the target discoveryrequest message. Accordingly, each of the types of UE performs theoperation of the 2 step. In this aspect, the ProSe discovery process ofFIG. 7 may be called a 2-step discovery procedure.

In addition to the discovery procedure described in FIG. 7, if the UE 1(the discoverer) sends a discovery conform message (may be hereinafterabbreviated as an M3), that is, a response to the target discoveryresponse message, this may be called a 3-step discovery procedure.

Meanwhile, a UE supporting D2D operation may provide relay functionalityto another network node (e.g., another UE or a base station).

FIG. 8 shows an example of the UE providing the relay functionality.

Referring to FIG. 8, UE2 153 performs a repeater function between thebase station 151 and UE1 152. That is, the UE2 153 may be referred to asa network node that performs a relay function between the UE1 152located outside the coverage 154 of the network and the network 151. D2Doperation may be performed between UE1 and UE2 152 and 153. Conventionalcellular communication or wide area network (WAN) communication may beperformed between UE2 153 and network 151. In FIG. 8, since UE1 152 islocated outside the network coverage, it cannot communicate with network151 if UE2 153 does not provide the relay function therebetween.

The present invention will now be described.

The present invention proposes a method for a UE to transmit asynchronization signal and a broadcast channel in order to perform a D2Doperation.

The UE may be a UE serving as a relay unit. In one example, a UE 1supporting D2D operation may perform a similar role as a repeaterbetween the UE 2 located outside the coverage of the network and thenetwork. That is, the UE 1 may receive a signal transmitted from thenetwork and send the signal to the UE 2 outside the coverage or mayreceive a signal transmitted by the UE 2 outside the coverage andtransmit the signal to the network. The D2D operation may be usedbetween the UEs 1 and 2.

Hereinafter, the UE performing the relay communication using the D2Doperation will be referred to as ‘D2D UE’, or ‘DRUE’. DRUE may transmita synchronization signal and a broadcast channel when performing relaycommunication using the D2D operation. Hereinafter, the synchronizationsignal used for the D2D operation will be referred to as SSS (SIDELINKSYNCHRONIZATION SIGNAL), and the broadcast channel used for the D2Doperation will be referred to as PSBCH (PHYSICAL SIDELINK BROADCASTCHANNEL), in order to distinguish from an existing synchronizationsignal and broadcast channel.

The SSS may include at least one of a PRIMARY SIDELINK SYNCHRONIZATIONSIGNAL (PSSS) and a SECONDARY SIDELINK SYNCHRONIZATION SIGNAL (SSSS).

Hereinafter, it is referred to as D2D communication that the UEcommunicates directly with another UE using a wireless channel(That is,in the following, the above-mentioned ProSe direct communication andProSe discovery are collectively referred to as D2D communication.) TheUE refers to the user device. However, a network equipment such as thebase station may be regarded as a kind of UE when the network equipmentsuch as the base station transmits/receives signals according to acommunication method between the UEs.

Hereinafter, the present invention will be described with reference tothe 3GPP LTE/LTE-A system for the convenience of description, but thescope of the system to which the present invention is applied is notlimited to the 3GPP LTE/LTE-A system and may be extended to othersystems.

An example of the PSBCH and SSS transmission operation/method is shownin the following table.

Referring to Table 1, the PSBCH may be transmitted through scrambling,modulation, layer mapping, transform precoding, precoding, mapping tophysical resources, and the like.

A block of bits b(0), . . . , b(M_(bit-1)) is scrambled using ascrambling sequence. Here, M_(bit) represents the number of bitstransmitted over the PBSCH in one subframe. The scrambling sequence usedfor scrambling may use a sequence generated based on the N^(SL) _(ID)for each subframe transmitting the PSBCH. PSBCH uses QPSK as modulationscheme. Layer mapping and precoding are performed using the assumptionof a single antenna port.

Next, a transmission method of the SSS will be described with referenceto Table 1 above.

The SSS may include PSSS and SSSS. PSSS may be transmitted using twoconcatenated SC-FDMA symbols in the same subframe, more specifically,the second and third SC-FDMA symbols in the first slot (this is true ofa normal CP; in an case of an extended CP, it may be transmitted usingthe first and second SC-FDMA symbols of the first slot). Two sequences,each having a length of 62 may be used for the two SC-FDMA symbols, anda root index of the sequences may be different between a case where theN^(SL) _(ID) is 167 and a case where the N^(SL) _(ID) is not 167. Here,the N^(SL) _(ID) may be a physical-layer sidelink synchronizationidentity, and may have a value from 0 to 335 or less. The N^(SL) _(ID)may be divided into id_net and id_oon, where id_net is a ID used in thecoverage and id_oon is a ID used outside the coverage. Id_net may have avalue from 0 to 167, and id_oon may have a value from 168 to 335.

SSSS may be transmitted using two concatenated SC-FDMA symbols in thesame subframe, more specifically, the fifth and sixth SC-FDMA symbols inthe second slot (this is true of a normal CP; in an case of an extendedCP, it may be transmitted using the fourth and fifth SC-FDMA symbols ofthe second slot). Two sequences, each having a length of 62 may be usedfor the two SC-FDMA symbols,

For convenience of explanation, some terms and situations to which thepresent invention is applied will be described.

FIG. 9 shows DL CARRIER#X, UL CARRIER#X, and CARRIER#Y set for DRUE#N.

Referring to FIG. 9, DRUE#N is assigned ‘DL CARRIER#X’, which is adownlink carrier related to WAN (wide area network communication), and‘UL CARRIER#X’, which is an uplink carrier related to WAN (wide areanetwork communication). Further, DRUE#N is assigned ‘CARRIER#Y’ relatedto D2D communication (or D2D relay communication). That is, DL CARRIER#Xand UL CARRIER#X are respectively downlink and uplink carriersconstituting a serving cell of DRUE#N (or for which the serving cell ofDRUE#N is present). CARRIER#Y is a carrier used for D2D communication.

Hereinafter, this situation is assumed and explained.

In D2D communication, the D2D communication related parameter values andthe operation procedures used may vary depending on whether the UE is innetwork (cell) coverage or outside the coverage. Thus, the UE may needto perform measurements in order to determine whether the UE is innetwork (cell) coverage or outside the coverage, to perform D2Dcommunication.

Hereinafter, based on (DL) CARRIER, measurements may be performed inorder to determine whether the UE is in network (cell) coverage oroutside the coverage, to perform D2D communication. Further, based on(DL) CARRIER, S-CRITERION (cell selection or reselection) may bedetermined. This (DL) CARRIER may be referred to as MEA_CARRIER.Further, based on the MEA_CARRIER, D2D communication related (downlink)measurement (e.g., (D2D transmission) power setting related PL(Pathloss) measurement) may be performed. Further, D2D communicationrelated (downlink) synchronization may be based on the MEA_CARRIER. TheMEA_CARRIER setting (or pairing) information may be communicated to theD2D UE via predefined signaling (e.g., SIB, RRC).

In the illustrated situation, in one example, DL CARRIER#X may beinterpreted as being set to MEA_CARRIER of UL CARRIER#X (and/orMEA_CARRIER of CARRIER#Y may be interpreted as being set to DLCARRIER#X).

Also, the DRUE#N may be interpreted as an IN-COVERAGE D2D UE in a(communication) coverage of a base station performing WAN communicationbased on DL CARRIER#X.

In the illustrated situation, it is assumed that there is no basestation performing WAN communication based on the correspondingCARRIER#Y. Accordingly, a D2D UE performing D2D communication only usingCARRIER#Y is regarded as ‘OUT-OF-COVERAGE (D2D UE)’.

CARRIER#Y may be interpreted as CARRIER (or resource) (or CARRIER whichnot assigned MEA_CARRIER) that is used only for D2D communication (orD2D relay communication).

In addition, for convenience of explanation, in one example, the OOC D2DUE that performs D2D RELAY communication with DRUE#N using CARRIER#Y isreferred to as ‘OOC D2D UE#K’ In FIG. 9, UE#K is OOC D2D UE#K. The OOCD2D UE#K may be interpreted as D2D UE as that does not find the basestation (or cell) on the DL CARRIER#X and performs the OOC D2Dcommunication on CARRIER#Y that has been preconfigured. The OOC D2D UE#Kmay be interpreted a D2D UE which cannot perform D2D communication inthe band to which UL CARRIER#X belongs due to RF Capability Limitation,but which is capable of performing D2D communication only in the band towhich CARRIER#Y belongs.

Hereinafter, the proposals of the present invention may be applied onlyin a limited manner to following cases: a case when DRUE#N performs D2Dcommunication (or D2D relay communication) only using CARRIER#Y and/or acase when DRUE#N performs D2D communication (or D2D relay communication)using both UL CARRIER#X and CARRIER#Y.

Also, the proposals of the present invention allow the OOC D2D UE#K toeffectively receive the D2D Relay communication related information (orthe D2D Relay communication data) by allowing DRUN#N to effectivelytransmit the SSS and/or the PSBCH when the DRUN#N carries out the D2DRelay communication on the CARRIER#Y. In one example, the DRUE#N may beinterpreted as an OUTBAND RELAY. Here, the OUTBAND RELAY may be definedas a repeater in which the first link between the base station and therepeater and the second link between the repeater and the UE are notoperated at the same frequency, or the first and second links aresufficiently isolated in the frequency domain such that interference isnot problematic although the two links are simultaneously activated.

The proposals of the present invention can be extended, in one example,when DRUE#N carries out D2D communication (or D2D relay communication)on CARRIER#Y. Alternatively, the proposals of the present invention maybe applied regardless of whether CARRIER#Y is assigned MEA_CARRIER (orwhether MEA_CARRIER of CARRIER#Y is set to DL CARRIER#X). Otherwise, theproposals of the present invention may be applied only a case whenCARRIER#Y is assigned MEA_CARRIER or when MEA_CARRIER of CARRIER#Y isset to DL CARRIER#X.

In addition, in one example, DRUE#N may be interpreted to relay DLCARRIER#X (which is MEA_CARRIER) (or UL CARRIER#X) related(system/relay) information (or (system/relay) information related to abase station performing WAN DL communication therewith using DLCARRIER#X) (to OOC D2D UE#K) using CARRIER#Y. In addition, in oneexample, DRUE#N may be interpreted to be in an RRC connection state(RRC_(—) CONNECTED) in the view of DL CARRIER#X (which is MEA_CARRIER)(or UL CARRIER#X) or in the view of a base station performing WAN DLcommunication therewith using DL CARRIER#X.

[The present method#1] When DRUE#N transmits a D2D Relay communicationrelated SSS and/or PSBCH using CARRIER#Y, it may be defined to followsome or all of the following rules.

Example#1

The ROOT SEQUENCE INDEX value for generation of the sequence of the PSSSmay be defined to use a value defined for an IN-COVERAGE (hereinafterreferred to as IC). In one example, the PSSS ROOT SEQUENCE INDEX valuefor the IC may be defined as 26, and the PSSS ROOT SEQUENCE INDEX valuefor the OOC may be defined as 37.

When such a rule is applied, the D2D Relay communication related PSSStransmitted by DRUE#N using CARRIER#Y may be regarded as the PSSStransmitted by the IC D2D UE in terms of OOC D2D UE#K. At this time, thePSSS transmission may be configured to be performed using IC SSSTRANSMISSION RESOURCE (or OSS SSS TRANSMISSION RESOURCE or D2D RELAYcommunication related SSS TRANSMISSION RESOURCE).

Example#2

The SIDELINK SYNCHRONIZATION IDENTITY (ID) value for generation of thesequence of the SSSS can be defined to use a value defined forin-coverage (IC). That is, the value of the specific ID used forgenerating the sequence of the SSSS is defined for and between thein-coverage purpose and the out-coverage purpose. When the DRUE#Ntransmits the D2D Relay communication related SSSS using the CARRIER#Y,ID for IC may be used. Here, in one example, the SIDELINKSYNCHRONIZATION ID value for IC is defined as {0, 1, . . . , 167} (seeid_net in Table 1). The SIDELINK SYNCHRONIZATION ID value for OOC is{168, 169, . . . 335} (see id_oon in Table 1).

When this rule is applied, the D2D RELAY communication related SSSS thatDRUE#N transmits using CARRIER#Y may be regarded as the SSSS transmittedby the IC D2D UE in terms of OOC D2D UE#K. Further, in one example, whenthis (example#2) is applied, the SSSS transmission may be configured tobe performed using the IC SSS TRANSMISSION RESOURCE (or OOC SSSTRANSMISSION RESOURCE or D2D RELAY communication related SSSTRANSMISSION RESOURCE).

Example#3

The CONTENTS transmitted through the PSBCH includes at least one of, inone example, DFN (D2D (SUB) FRAME NUMBER), TDD UL-DL CONFIGURATION,IN-COVERAGE INDICATOR, SIDELINK SYSTEM BANDWIDTH and RESERVED FIELD.Among these, if the IN-COVERAGE INDICATOR has a specific value (in oneexample, ‘1’), it may notify that the PSBCH is a D2D signal transmittedfrom the IC D2D UE. When DRUE#N may transmit the D2D Relay communicationrelated PSBCH using CARRIER#Y, the DRUE#N may set the IN-COVERAGEINDICATOR to ‘1’. In this case, the D2D Relay communication relatedPSBCH transmitted by DRUE#N using CARRIER#Y may be regarded as the PSBCHtransmitted by the IC D2D UE in view of the OOC D2D UE#K.

In another example, by setting the RESERVED FIELD in the CONTENTStransmitted via the PSBCH to a predefined value, the PSBCH may bedefined to be interpreted as the PSBCH transmitted by the D2D RELAY UE(or (REL-13) IC D2D UE) in terms of OOC D2D UE#K.

Also, in one example, when this (example#3) is applied, the PSBCHtransmission may be configured to be performed using the IC SSSTRANSMISSION RESOURCE (or OOC SSS TRANSMISSION RESOURCE or D2D RELAYcommunication related SSS TRANSMISSION RESOURCE).

Example#4

Through predefined signaling, DRUE#N may be informed which CARRIER isthe MEA_CARRIER of CARRIER#Y.

In one example, if MEA_CARRIER of CARRIER#Y is set (or signaled) to DLCARRIER#X, DRUE#N is allowed to configure/transmit the D2D RELAYcommunication related SSS and/or PSBCH transmitted using CARRIER#Y inthe same manner as in IC. Here, in one example, the corresponding SSSand/or PSBCH transmission may be configured to be performed using the ICSSS TRANSMISSION RESOURCE (or OSS SSS TRANSMISSION RESOURCE or D2D RELAYcommunication related SSS TRANSMISSION RESOURCE).

On the other hand, if MEA_CARRIER of CARRIER#Y is not set (or signaled)(or MEA_CARRIER of CARRIER#Y is not set (or signaled) to DL CARRIER#X),DRUE#N is allowed to configure/transmit the D2D RELAY communicationrelated SSS and/or PSBCH transmitted using CARRIER#Y in the same manneras in OCC.

Here, in one example, the corresponding SSS and/or PSBCH transmissionmay be configured to be performed using an OCC SSS TRANSMISSION RESOURCE(or IC SSS TRANSMISSION RESOURCE or D2D RELAY communication related SSSTRANSMISSION RESOURCE). In another example, a transmission operationusing CARRIER#Y may be determined based on MEASUREMENT and S-CRITERIONsatisfaction for MEA_CARRIER of the CARRIER#Y, as designated via theMEA_CARRIER setting related signaling (in one example, ROOT SEQUENCEINDEX for generating a PSSS sequence and/or SIDELINK SYNCHRONIZATION IDfor SSSS sequence generation may be determined based on determinationabout whether it is IC or OCC).

FIG. 10 illustrates a specific method using the example#4 above.

Referring to FIG. 10, the user device (DRUE#N) determines whether thereis an active serving cell on a non-primary carrier that is not a primarycarrier to perform a D2D operation (S190). In one example, suppose thatthe user device has an RRC connection state with a specific base stationusing DL carrier#X, and UL carrier#X, and wants to transmit a D2Ddiscovery signal using the carrier#Y. In this case, the user devicedetermines whether or not there is an activated serving cell on thecarrier#Y.

If there is a serving cell activated on the non-primary carrier, theuser device uses the activated serving cell for downlink measurement andsynchronization for D2D operation (S191).

On the other hand, if there is no serving cell activated on thenon-primary carrier, the user device uses one downlink carrier indicatedby the current serving cell (base station) for downlink measurement andsynchronization for D2D operation (S192). The one downlink carrier maybe a DL carrier (e.g., a DL carrier linked by system information) thatis one of a pair of carriers via which the user device performs the D2Doperation (e.g., D2D discovery signal transmission) or may be a DLcarrier without this limitation (that is, a DL carrier that is notlinked by system information).

FIG. 11 illustrates a method of transmitting a D2D discovery signal bythe user device according to an embodiment of the present invention.

Referring to FIG. 11, DRUE#N transmits D2D INTEREST information to aserving cell (base station) (S111). The D2D INTEREST information may beinformation that informs the serving cell that DRUE#N is interested inD2D operation on a particular carrier. In one example, DRUE#N may informthe serving cell that it is interested in transmitting a D2D discoverysignal using CARRIER#Y rather than DL CARRIER#X, and UL CARRIER#X, whichare carriers that are performing WAN communication with the servingcell. The D2D INTEREST information may be provided separately from thecapability information of the user device (UE CAPABILITY INFORMATION) orincluded in the user device capability information.

The serving cell provides MEA_CARRIER indication information indicatingthe measured carrier (MEA_CARRIER) to DRUE#N (S112). In the aboveexample, DRUE#N may be informed that MEA_CARRIER for CARRIER#Y is DLCARRIER#X.

DRUE#N may measure the DL CARRIER indicated by the MEA_CARRIERindication information and perform synchronization based on the DLCARRIER (S113). Here, it may be assumed that there is no active servingcell using CARRIER#Y for DRUE#N. If there is an active serving cellusing CARRIER#Y for DRUE#N, then the activated serving cell is used fordownlink measurement and synchronization for D2D operation.

DRUE#N transmits a D2D discovery signal to UE#K based on the downlinkmeasurement and synchronization (S114). As an additional example, DRUE#Nmay perform coverage-in/out determination for the DL CARRIER#X, tothereby use either the D2D parameter in coverage or the D2D parameteroutside of coverage for the D2D operation using CARRIER#Y.

Example#5

The UE may be configured to configure/transmit the D2D RELAYcommunication related SSS and/or PSBCH according to some or all of thefollowing rules.

1) The ROOT SEQUENCE ID for generating the sequence of PSSS and/or theSIDELINK SYNCHRONIZATION ID for SSSS sequence generation use what isdefined for the OOC purpose, but the RESERVED FIELD in the CONTENTStransmitted through PSBCH is set to the predefined value (or IN-COVERAGEINDICATOR is set to 1). Thus, it may be interpreted from the point ofview of the OOC D2D UE#K that the corresponding D2D RELAY communicationrelated SSS and/or PSBCH is transmitted from D2D RELAY UE or (REL-13) ICD2D UE.

As another example, the ROOT SEQUENCE ID for generating the sequence ofPSSS and/or the SIDELINK SYNCHRONIZATION ID for SSSS sequence generationuse what is defined for the IC purpose, and the RESERVED FIELD in theCONTENTS transmitted through PSBCH is set to the predefined value (orIN-COVERAGE INDICATOR is set to 0). Thus, it may be interpreted from thepoint of view of the OOC D2D UE#K that the corresponding D2D RELAYcommunication related SSS and/or PSBCH is transmitted from D2D RELAY UEor (REL-13) IC D2D UE.

2) The ROOT SEQUENCE ID for generating the sequence of PSSS and/or theSIDELINK SYNCHRONIZATION ID for SSSS sequence generation use what isdefined for the IC purpose, and the IN-COVERAGE INDICATOR in theCONTENTS transmitted through PSBCH is set to 1 (or the RESERVED FIELD isset to the predefined value). Thus, it may be interpreted from the pointof view of the OOC D2D UE#K that the corresponding D2D RELAYcommunication related SSS and/or PSBCH is transmitted from D2D RELAY UEor (REL-13) IC D2D UE.

3) As another example, the ROOT SEQUENCE ID for generating the sequenceof PSSS and/or the SIDELINK SYNCHRONIZATION ID for SSSS sequencegeneration use what is defined for the IC (or OOC) purpose, and theSIDELINK SYNCHRONIZATION ID (see Table 1) used for the initialization ofthe PSBCH SCRAMBLING SEQUENCE GENERATOR may be defined to use (orsubstitute) a pre-configured (or signaled) D2D RELAYcommunication-related SIDELINK SYNCHRONIZATION ID value.

Here, in one example, the DID Relay communication-related SIDELINKSYNCHRONIZATION ID value may be set (or signaled) to one of the SIDELINKSYNCHRONIZATION IDs (e.g., {168, 169, . . . , 335}) for OCC (See id_oonin Table 1) or may be set (or signaled) to one of the SIDELINKSYNCHRONIZATION IDs for IC (e.g., {0, 1, . . . , 167} (See id_net inTable 1).

Example#6

The SIDELINK SYNCHRONIZATION ID used in the determination of the ROOTSEQUENCE INDEX related to the PSSS sequence generation and/or theSIDELINK SYNCHRONIZATION ID used for generating the SSSS sequence (seeTable 1) may be configured to use (or substitute) the SIDELINKSYNCHRONIZATION ID value (e.g., {168, 169, . . . , 335} (see id_oon inTable 1) as preconfigured or pre-signaled for OOC. Here, in one example,a rule may be defined to pre-signal (or preset) SSS (and/or PSBCH)transmission related resources. When such a rule is applied, in oneexample, DRUE(s) that transmits a D2D RELAY communication related SSS(and/or PSBCH) using CARRIER#Y may be configured to use the sameSIDELINK SYNCHRONIZATION ID for PSSS and/or SSSS sequence generationand/or PSBCH SCRAMBLING SEQUENCE GENERATOR initialization.

In addition, such a rule causes the UE performing the OUTBAND D2D RELAYto transmit the PSSS and/or SSSS sequence for the OOC purpose. However,the SIDELINK SYNCHRONIZATION ID and the resources (related to the PSSSand/or SSSS transmission) may be interpreted to be signaled from thebase station. In addition, if such a rule applies, in one example,DRUE(s) that transmits a D2D RELAY communication related SSS (and/orPSBCH) using CARRIER#Y may be configured to transmit the D2D Relaycommunication related SSS (and/or PSBCH) using the same resources. Asanother example, the SIDELINK SYNCHRONIZATION ID used for determinationof the ROOT SEQUENCE INDEX related to the PSSS sequence generationand/or the SIDELINK SYNCHRONIZATION ID used for the SSSS sequencegeneration may be configured to use (or substitute) the SIDELINKSYNCHRONIZATION ID value (e.g., {0, 1, . . . , 167} (see id_net inTable 1) as preconfigured or pre-signaled for IC.

In one example, if the OOC D2D UE#K receives from the DRUE#N, a SSSand/or a PSBCH to which some or all rules of the above-described [thepresent Method#1] are applied, the corresponding D2D Relay communicationrelated SSS and/or PSBCH may be defined to have SYNCHRONIZATION SOURCESELECTION PRIORITY higher than those received from other OOC D2D UEsusing the CARRIER#Y (or may be defined to have PRIORITY higher thanthose received from other OOC D2D UEs using the CARRIER#Y in terms ofD2D Relay communication related SSS and/or PSBCH and/or DATA and/orDISCOVERY receipt).

As another example, if the OOC D2D UE#K receives from the DRUE#N, a SSSand/or a PSBCH to which some or all rules of the above-described [thepresent Method#1] are applied, the corresponding D2D Relay communicationrelated SSS and/or PSBCH may be defined to have SYNCHRONIZATION SOURCESELECTION PRIORITY higher than those received from other OOC D2D UEsusing the CARRIER#Y but to have SYNCHRONIZATION SOURCE SELECTIONPRIORITY higher than those received from other IC D2D UEs using theCARRIER#Y. Here, in one example, these rules may be applicable tofollowing cases: 1) case when there are base stations performing WANcommunication based on CARRIER#Y and, thus, PARTIAL COVERAGE SCENARIOmay occur; 2) a case in which when DRUE#N configures/transmits the D2DRELAY communication-related SSS and/or PSBCH, the ROOT SEQUENCE ID forgenerating the sequence of PSSS and/or the SIDELINK SYNCHRONIZATION IDfor SSSS sequence generation use what is defined for the IC purpose, andthe IN-COVERAGE INDICATOR in the CONTENTS transmitted through PSBCH isset to 0 (or the RESERVED FIELD is set to the predefined value).

As another example, if DRUE#N is performing D2D communication using ULCARRIER#X as well as CARRIER#Y, a rule may be configured such that theD2D transmission (TX) operation (and/or D2D reception (RX) operation)using CARRIER#X may have a higher PRIORITY than the D2D transmission(TX) operation (and/or D2D reception (RX) operation) using CARRIER#Y.Here, in one example, the application of such a rule may result ininterpretation that IC D2D TX operation (and/or IC D2D RX operation)(that is, D2D communication using UL CARRIER#X) has a higher prioritythan D2D RELAY communication using CARRIER#Y.

As further example, if DRUE#N does not have the capability tosimultaneously perform D2D communication using UL CARRIER#X andCARRIER#Y, the D2D RELAY communication (or D2D RELAY operation) usingCARRIER#Y may be suppressed during a period in which D2D communicationis performed using UL CARRIER#X.

As another example, if DRUE#N is performing D2D communication using ULCARRIER#X as well as CARRIER#Y, a rule may be configured such that theD2D transmission (TX) operation (and/or D2D reception (RX) operation)using CARRIER#Y may have a higher PRIORITY than the D2D transmission(TX) operation (and/or D2D reception (RX) operation) using CARRIER#X. Inone example, if DRUE#N does not have the capability to simultaneouslyperform D2D communication using UL CARRIER#X and CARRIER#Y, the D2DRELAY communication (or D2D RELAY operation) using CARRIER#X may besuppressed during a period in which D2D communication is performed usingUL CARRIER#Y. This rule may be applied only to following cases: a casewhen the MEA_CARRIER of CARRIER#Y is set to DL CARRIER#X throughpredefined signaling, or a case when the DRUE#N relays (system)information of a base station performing WAN communication based on DLCARRIER#X using the CARRIER#Y.

In another example, the DRUE may use the predefined method (or rule) toindicate the presence thereof to other D2D OOC UEs, even though the DRUEdoes not have the information to be transmitted to other D2D OOC UEs (orPSCCH (PHYSICAL SIDELINK CONTROL CHANNEL)/PSSCH (PHYSICAL SIDELINKSHARED CHANNEL)). In this way, the OOC D2D UE can detect thecorresponding DRU and transmit DATA thereto to support (or perform) theRELAY operation with the network. Here, in one example, DRUE mayannounce its existence to the other D2D OOC UEs by sending a predefinedspecial PSCCH and/or SSS (for a pre-defined (or signaled) time/period,even though the DRUE does not have the information to be transmitted toother D2D OOC UEs (or PSCCH (PHYSICAL SIDELINK CONTROL CHANNEL)/PSSCH(PHYSICAL SIDELINK SHARED CHANNEL)). Here, in one example, a groupdestination ID field (GROUP DESTINATION ID FIELD) on the correspondingPSCCH may be set to the predetermined (or signaled) special value. Inparticular, in one example, the proposed scheme may be applicable notonly to OUTBAND D2D RELAY but also to INBAND D2D RELAY. Here, the INBANDRELAY may be defined as a repeater when the link between the basestation and the repeater and the link between the repeater and the userdevice share the same carrier frequency.

As another example, DRUE may be configured to send the predefinedspecial PSCCH (for a predefined (or signaled) time/period) regardless oftraffic, thereby to ensure that DRUE may reliably send SSS (for thepredefined (or signaled) time/period). Here, in one example, the GROUPDESTINATION ID FIELD on the PSCCH may be set to a predefined (orsignaled) specific value. As another example, DRUE may be configured toperform an SSS transmission for a predefined (or signaled) time/periodeven though there is no information to be transmitted to other D2D OOCUEs (or PSCCH/PSSCH).

As another example, when DRUE#N performs D2D RELAY communication (or D2Dcommunication) using CARRIER#Y based on some or all of theabove-described suggested rules, some or all information in thefollowing examples#A to#E may be defined such that they are set (orassumed) to be the same as those for MEA_CARRIER of CARRIER#Y (or apredefined or signaled specific CARRIER, wherein WAN DL communicationmay be performed using the specific CARRIER).

Example#A

DFN (D2D frame number) information. Among the PSBCH CONTENTS transmittedusing CARRIER#Y, the DFN field may be set equally to the SFN (SYSTEM(SUB) FRAME NUMBER) of the corresponding MEA_CARRIER. In this case, theD2D RELAY communication (or D2D communication) related time/frequencysynchronization using CARRIER#Y may be interpreted as equal to that forthe MEA_CARRIER.

Example#B

TDD UL-DL CONFIGURATION information. If the MEA_CARRIER of CARRIER#Y isan FDD CARRIER, the TDD UL-DL CONFIGURATION field in the PSBCH CONTENTStransmitted using CARRIER#Y is set to ‘000’. If MEA_CARRIER of CARRIER#Yis TDD CARRIER, the TDD UL-DL CONFIGURATION field in the PSBCH CONTENTStransmitted using CARRIER#Y may be set to equally point to the TDD UL-DLCONFIGURATION of the corresponding MEA_CARRIER. In another example, theTDD UL-DL CONFIGURATION field in the PSBCH CONTENTS transmitted usingCARRIER#Y may be a FDD CARRIER (/BAND) or a CARDER_CONDITION field maybe configured such that the corresponding TDD UL-DL CONFIGURATION fieldvalue is determined depending on whether the CARRIER#Y is a TDD CARRIER(/BAND) or PM CARRIER (/BAND), regardless of whether the MEA_CARRIER isa FDD CARRIER or a TDD CARRIER.

In another example, if the TDD UL-DL CONFIGURATION field in the PSBCHCONTENTS transmitted using CARRIER#Y indicates a TDD system (or (actual)TDD UL-DL CONFIGURATION) according to the proposed rule,interworking/matching relationship between the TIME RESOURCE PATTERNfield value on the PSCCH (SCI FORMAT 0) and the SUBFRAME INDICATORBITMAP, which determines the time resolution pattern of the (MODE1)PSSCH transmitted using CARRIER#Y may be defined with reference to TABLEdefined for performing D2D communication on the TDD system (as definedin the 3GPP TS 36.213 specification). To the contrary, if the TDD UL-DLCONFIGURATION field in the PSBCH CONTENTS transmitted using CARRIER#Yindicates FDD system (i.e., ‘000’), the interworking/matchingrelationship between the TIME RESOURCE PATTERN field value on the PSCCH(SCI FORMAT 0) and the SUBFRAME INDICATOR BITMAP, which determines thetime resolution pattern of the (MODE1) PSSCH transmitted using CARRIER#Ymay be defined with reference to TABLE defined for performing D2Dcommunication on the FDD system (as defined in the 3GPP TS 36.213specification). In still another example, if the TDD UL-DL CONFIGURATIONfield in the PSBCH CONTENTS transmitted using CARRIER#Y indicates(actual) TDD UL-DL CONFIGURATION or TDD system according to the proposedrule, the TIME RESOURCE PATTERN candidates (i.e., ‘ITRP’ [1]) of MODE2PSSCH may be defined to assume (or refer to) those matching thecorresponding TDD UL-DL CONFIGURATION. To the contrary, if the TDD UL-DLCONFIGURATION field in the PSBCH CONTENTS transmitted using CARRIER#Yindicates FDD system (i.e., ‘000’), the TIME RESOURCE PATTERN candidates(i.e., ‘ITRP’ [1]) of MODE2 PSSCH may be defined to assume (or refer to)those matching the corresponding FDD UL-DL CONFIGURATION.

Example#C

IN-COVERAGE INDICATOR information. Among the PSBCH CONTENTS transmittedusing CARRIER#Y, the IN-COVERAGE INDICATOR field may be set according tothe IN/OOC status for the corresponding MEA_CARRIER.

Example#D

CARRIER#Y's MEA_CARRIER (or a predefined (or signaled) specific CARRIER(to which WAN DL communication is performed) and PAIRED UL CARRIERrelated DISCOVERY and/or COMMUNICATION and/or SSS/PSBCH transmission(and/or receiving) related RESOURCE POOL setting information.

Example#E

Time (or subframe or radio frame) (and/or frequency) synchronization. Asanother example, the rule may be defined to (always) synchronize time(or subframe or radio frame) to PCell (or RELAY communication relatedSCI FORMAT 0 (D2D GRANT) transmission related SCHEDULING CELL (i.e.,MODE 1)) regardless of MEA_CARRIER.

As another example, a rule may be defined such that regardless ofwhether MEA_CARRIER of CARRIER#Y is a TDD/FDD CARRIER, at least one ofthe TDD UL-DL CONFIGURATION field, the DFN field, the IN-COVERAGEINDICATOR field, the SIDELINK SYSTEM BANDWIDTH, and the RESERVED FIELDsin the PSBCH CONTENTS transmitted using CARRIER#Y may be set (or fixed)to a predefined (or signaled) value Here, as an example of theapplication of the proposed scheme, the TDD UL-DL CONFIGURATION field inthe PSBCH CONTENTS transmitted using CARRIER#Y may be set or fixed to apredefined (or signaled) ‘000’ is. In this case, CARRIER#Y may beinterpreted as a (virtual) FDD UL CARRIER. As another example, a rulemay be defined such that when DRUE#N performs D2D RELAY communication(based on MODE1) using CARRIER#Y, it transmits SCI FORMAT 0 (D2D GRANT)(related to RELAY communication) based on CROSS CARRIER SCHEDULING usingother CARRIERs.

As another example, when the D2D UE#X performs D2D communication using apreset (or signaled) CARRIER#T and CARRIER#F, if the CARRIER#F isconsidered (or determined) for OOC and the CARRIER#T is considered (ordetermined) for IC, transmission of at least one of SSS, PSBCH, PSCCH,PSSCH, and PSDCH (PHYSICAL SIDELINK DISCOVERY CHANNEL) using CARRIER#Fmay be done according to some or all of the following rules/assumptions.Here, in one example, CARRIER#F may be interpreted as a CARRIERdedicated to V2V communication (VEHICLE TO VEHICLE communication, whichmay be interpreted as direct communication between vehicles). Also, byway of example, these rules/assumptions may be used only when D2D UE#Xdoes not perform D2D RELAY communication (using CARRIER#F) (or if D2DUE#X is not set to DRUE using CARRIER#F).

Example#A

The SIDELINK SYNCHRONIZATION ID used in the determination of the ROOTSEQUENCE INDEX related to the generation of the PSSS sequencetransmitted using CARRIER#F, and/or the SIDELINK SYNCHRONIZATION ID (seeTable 1) used for generating the SSSS sequence may be configured to useSIDELINK SYNCHRONIZATION ID values (in one example, {168, 169, . . . ,335} (see id_oon in Table 1) as pre-signaled (or preset) for OOC. Here,in one example, SSS (and/or PSBCH) transmission related resources mayalso be pre-signaled (or preset). If such a rule applies, in oneexample, a D2D UE(s) that transmits an SSS (and/or PSBCH) (related toV2V communication) using CARRIER#F (for V2V communication only) may beconfigured to use the same SIDELINK SYNCHRONIZATION ID for generation ofPSSS and/or SSSS sequence (and/or for initialization of the PSBCHSCRAMBLING SEQUENCE GENERATOR). In addition, if such a rule applies, inone example, a D2D UE(s) that transmits an SSS (and/or PSBCH) (relatedto V2V communication) using CARRIER#F (for V2V communication only) maybe configured to transmit the corresponding SSS (and/or PSBCH) using thesame resources. In another example, the SIDELINK SYNCHRONIZATION ID usedin the determination of the ROOT SEQUENCE INDEX related to thegeneration of the PSSS sequence transmitted using CARRIER#F, and/or theSIDELINK SYNCHRONIZATION ID used for generating the SSSS sequence may beconfigured to use SIDELINK SYNCHRONIZATION ID values (in one example,{0, 1, . . . , 167} (see id_net in Table 1) as pre-signaled (or preset)for IC.

Example#B

Some or all of the following information (that is, at least one of theexamples#B-1 to#B-5 to be described later) relating to thepre-established (or pre-signaled) CARRIER (referred to as ‘REF_CARRIER’)may be equally applied to the transmission of at least one of the SSS,PSBCH, PSCCH, PSSCH and PSDCH using the CARRIER#F. For example,REF_CARRIER may be defined as a PCell or a SCHEDULING CELL (i.e.,MODE 1) associated with (V2V communication-related) SCI FORMAT 0 (D2DGRANT) transmission regardless of whether it is MEA_CARRIER of CARRIER#For UL CARRIER paired with MEA_CARRIER of CARRIER#T (or a predefined (orsignaled) specific CARRIER (via which WAN DL communication isperformed)).

Example#B-1

DFN information. Here, in one example, among the PSBCH CONTENTStransmitted using CARRIER#F, the DFN field may be set equally to the SFN(SYSTEM (SUB) FRAME NUMBER) of the corresponding REF_CARRIER. In thiscase, the D2D communication related time (/frequency) synchronizationusing CARRIER#F may be interpreted as being equal to that using theREF_CARRIER.

Example#B-2

TDD UL-DL CONFIGURATION information. For example, if REF_CARRIER ofCARRIER#F is 1-DD CARRIER, the TDD UL-DL CONFIGURATION field in PSBCHCONTENTS transmitted using CARRIER#F is set to ‘000’. When REF_CARRIERof CARRIER#F is TDD CARRIER, the TDD UL-DL CONFIGURATION field in PSBCHCONTENTS transmitted using CARRIER#F may be set to equally point to theTDD UL-DL CONFIGURATION of the corresponding REF_CARRIER. As anotherexample, the TDD UL-DL CONFIGURATION field in the PSBCH CONTENTStransmitted using CARRIER#F may be configured such that thecorresponding TDD UL-DL CONFIGURATION field value is determined based onwhether CARRIER#is a FDD CARRIER (BAND) or a TDD CARRIER (BAND)regardless of whether the REF_CARRIER is an FDD CARRIER or a TDDCARRIER. As another example, if the TDD UL-DL CONFIGURATION field inPSBCH CONTENTS transmitted using CARRIER#F indicates a TDD system (or(actual) TDD UL-DL CONFIGURATION) according to the proposed rule,interworking/matching relationship between the TIME RESOURCE PATTERNfield value on the PSCCH (SCI FORMAT 0) and the SUBFRAME INDICATORBITMAP, which determines the time resolution pattern of the (MODE1)PSSCH transmitted using CARRIER#Y may be defined with reference to TABLEdefined for performing D2D communication on the TDD system (as definedin the 3GPP TS 36.213 specification). To the contrary, if the TDD UL-DLCONFIGURATION field in PSBCH CONTENTS transmitted using CARRIER#Findicates a FDD system (i.e., ‘000’), the interworking/matchingrelationship between the TIME RESOURCE PATTERN field value on the PSCCH(SCI FORMAT 0) and the SUBFRAME INDICATOR BITMAP, which determines thetime resolution pattern of the (MODE1) PSSCH transmitted using CARRIER#Ymay be defined with reference to TABLE defined for performing D2Dcommunication on the FDD system (as defined in the 3GPP TS 36.213specification). In still another example, if the TDD UL-DL CONFIGURATIONfield in the PSBCH CONTENTS transmitted using CARRIER#Y indicates(actual) TDD UL-DL CONFIGURATION or TDD system according to the proposedrule, the TIME RESOURCE PATTERN candidates (i.e., ‘ITRP’ [1]) of MODE2PSSCH may be defined to assume (or refer to) those matching thecorresponding TDD UL-DL CONFIGURATION. To the contrary, if the TDD UL-DLCONFIGURATION field in the PSBCH CONTENTS transmitted using CARRIER#Yindicates FDD system (i.e., ‘000’), the TIME RESOURCE PATTERN candidates(i.e., ‘ITRP’ [1]) of MODE2 PSSCH may be defined to assume (or refer to)those matching the corresponding FDD UL-DL CONFIGURATION.

Example#B-3

IN-COVERAGE INDICATOR information. Here, for example, among the PSBCHCONTENTS transmitted using CARRIER#F, the IN-COVERAGE INDICATOR fieldmay be set according to the IN/OOC status of the correspondingREF_CARRIER.

Example#B-4

RESOURCE POOL setting information related to REF_CARRIER relatedDISCOVERY and/or COMMUNICATION and/or SSS/PSBCH transmission (and/orreception).

Example#B-5

Time (or subframe or radio frame) (and/or frequency) synchronization. Asanother example, a rule may be defined to synchronize (always) time (orsubframe or radio frame) to REF_CARRIER.

In the following, it is assumed that the user device performs D2Doperation in CARRIER#X. When TIMING REFERENCE (CELL) associated with theD2D TX and/or D2D RX operation using CARRIER#X (for example, SCELL (orNON-PCELL) or NON-SERVING CELL) is set or signaled to PCELL (hereinafterreferred to as REFER_CELL) (or other CARRIER (as pre-signaled orpredefined) other than CARRIER#X and/or when the RESOURCE POOLinformation associated with the D2D TX and/or D2D RX operation usingCARRIER#X is received (or CROSS-CARRIER-signaled) from the REFER_CELLother than the CARRIER#X, some or all of the following rules may bedefined to be applied thereto.

That is, when the UE is set to comply with the time reference of acarrier other than the carrier wave CARRIER#X performing the D2Doperation (more specifically, the time reference of a cell using theother carrier) or to receive the resource pool information from the cellusing the other carrier wave, some or all of the following rules may bedefined to be applied thereto. The cell using the other carrierproviding the time reference or providing the resource pool informationwill be referred to as a reference cell (REFER_CELL) hereinafter. Therules to be described later may be defined to be limited to the userdevice in the RELL connection state in the PCELL and/or the user devicein the RRC idle state in the PCELL.

(Rule 1-1) REFER_CELL indicates CARRIER#X-based OOC D2D communicationrelated RESOURCE POOL information and SIDELINK SYNCHRONIZATION SIGNAL ID(SLSSID), together with CARRIER#X-based IN-COVERAGE (INC) D2Dcommunication related RESOURCE POOL information and SLSSID information,and the like. This considers the possibility that D2D communicationusing CARRIER#X becomes OUT-OF-COVERAGE (OOC) from the viewpoint of D2DUE.

From the viewpoint of the D2D UE, when the D2D communication using theCARRIER#X becomes OOC, the UE follows (exceptionally) the (CARRIER#Xbased) TIMING in the OOC situation rather than the REFER CELL basedTIMING REFERENCE (and/or TA), and further, a rule may be defined toperform OOC D2D communication using CARRIER#X based on OOC D2Dcommunication related RESOURCE POOL information and SLSSID received fromthe REFER_CELL. In an alternative, the UE may comply with REFER_CELLbased TIMING REFERENCE (TA) or comply with both of REFER_CELL basedTIMING REFERENCE and (CARRIER#X based) TA setting in an OOC situation,and, further, the rule may be defined to perform OOC D2D communicationusing CARRIER#X based on OOC D2D communication related RESOURCE POOLinformation and SLSSID received from the REFER_CELL. As another example,when a D2D communication using CARRIER#X is INC from the viewpoint of aD2D UE, the UE may comply with REFER_CELL based TIMING REFERENCE (TA)(or comply with both of REFER_CELL based TIMING REFERENCE and (CARRIER#Xbased) TA setting in an OOC situation), and, further, the rule may bedefined to perform INC D2D communication using CARRIER#X based on INCD2D communication related RESOURCE POOL information and SLSSID receivedfrom the REFER_CELL.

(Rule 1-2) REFER_CELL indicates D2D UE of at least one of commonRESOURCE POOL information and SLSSID information to be commonly used forOOC D2D communication and INC D2D communication using the CARRIER#X.Thus, D2D UE may perform at least one of CARRIER#X-based OOC D2Dcommunication and INC D2D communication based on the indicated RESOURCEPOOL information and SLSSID information.

In one example, if a D2D communication using CARRIER#X is OOC from aviewpoint of an D2D UE, the UE follows (exceptionally) the (CARRIER#Xbased) TIMING in the OOC situation rather than the REFER_CELL basedTIMING REFERENCE (and/or TA), and further, the UE may perform OOC D2Dcommunication using CARRIER#X based on (common) D2D communicationrelated RESOURCE POOL information and SLSSID received from theREFER_CELL. In an alternative, the UE may comply with REFER_CELL basedTIMING REFERENCE (TA) or comply with both of REFER_CELL based TIMINGREFERENCE and (CARRIER#X based) TA setting in an OOC situation, and,further, the UE may perform OOC D2D communication using CARRIER#X basedon (common) D2D communication related RESOURCE POOL information andSLSSID received from the REFER_CELL. As another example, when a D2Dcommunication using CARRIER#X is INC from the viewpoint of a D2D UE, theUE may comply with REFER_CELL based TIMING REFERENCE (TA) (or complywith both of REFER_CELL based TIMING REFERENCE and (CARRIER#X based) TAsetting in an OOC situation), and, further, the UE may perform INC D2Dcommunication using CARRIER#X based on (common) D2D communicationrelated RESOURCE POOL information and SLSSID received from theREFER_CELL.

On the other hand, when the NON-SERVING CELL (and/or SCELL) performingD2D TX (/RX) operation is determined (or assumed) to be IN-COVERAGE,frequency synchronization and/or time synchronization related to D2D TX(/RX) operation in the NON-SERVING CELL may be done in accordance withall or some of the following rules.

Here, it is assumed that the SERVING CELL (and/or PCELL) and theNON-SERVING CELL (and/or SCELL) use (or belong to) different CARRIERs.In addition, some or all of the following rules may apply only to a casewhen CARRIER associated with the NON-SERVING CELL (and/or SCELL) andCARRIER associated with SERVING CELL (and/or PCELL) have INTER-BAND(and/or INTRA-BAND CONTIGUOUS and/or INTRA-BAND NON-CONTIGUOUS)relationship.

FIG. 12 illustrates a situation in which the user device performs a D2Doperation.

Referring to FIG. 12, the user device may be required to perform a D2Doperation at the F2 frequency while having a specific cell serving as aserving cell (or PCELL) at F1 frequency. The user device may be locatedwithin the coverage of the NON-SERVING CELL (or SCELL) at F2 frequency.The NON-SERVING CELL (or SCELL) at the F2 frequency may be referred toas an IN-COVERAGE NON-SERVING CELL (or IN-COVERAGE SCELL).

In the situation described in FIG. 12, when the user device attempts toperform the D2D operation, how to control frequency synchronization andtime synchronization is an issue. Hereinafter, this issue will bedescribed in detail.

(Rule#A-1) In performing the D2D operation (D2D transmission or D2Dreception), the user device adjusts frequency synchronization and timesynchronization according to predefined rules (or signaled information)and then transmits D2D signals. The user device may apply frequencysynchronization related to D2D TX (/RX) operation on the correspondingNON-SERVING CELL (and/or SCELL) according to IN-COVERAGE NON-SERVINGCELL (and/or SCELL). In addition, the D2D TX (/RX) operation timesynchronization on the corresponding non-serving cell (and/or SCELL) maybe (further) applied or assumed according to the IN-COVERAGE NON-SERVINGCELL (and/or SCELL).

(Rule#A-2) The user device may apply or assume synchronization of theD2D TX (/RX) operation on the corresponding NON-SERVING CELL (and/orSCELL) according to the IN-COVERAGE NON-SERVING CELL. In thisconnection, frequency synchronization may be defined to follow PCELL(and/or SERVING CELL). That is, in FIG. 12, the user device adjusts thefrequency synchronization according to the serving cell (PCELL) at theF1 frequency, adjusts the time synchronization according to theNON-SERVING CELL at the F2 frequency, and then performs the D2Doperation.

FIG. 13 is a method for performing the D2D operation by the user devicewhen Rule#A-2 is applied.

Referring to FIG. 13, the user device applies frequency synchronizationbased on a primary cell (or serving cell) at a first frequency (S210).The user device applies time synchronization based on the NON-SERVINGCELL (or SCELL) at the second frequency F2 intending to perform the D2Doperation (S220).

The user device performs the D2D operation by applying the frequencysynchronization and the time synchronization (S230).

For example, the user device, which is in the RRC connection state witha specific cell at frequency#1 as the PCELL (or serving cell), desiresto perform the D2D operation at frequency#2. In this connection, thecells at the frequency#2 may be NON-SERVING CELL (or SCELL) for the userdevice. The user device may be within the coverage of the NON-SERVINGCELL (or SCELL). In this case, the user device adjusts the frequencysynchronization for the D2D operation based on the PCELL (or servingcell) and adjusts the time synchronization based on the NON-SERVING CELL(or SCELL) at the frequency#2.

Rule#A-2 described above may be applied to a case when SEARCHING WINDOWSIZE (related to the corresponding NON-SERVING CELL) (or REFERENCESYNCHRONIZATION WINDOW SIZE) is signaled (or indicated) to have W2 (<CPLENGTH) (that is, when the difference between the frequency (/time)synchronization according to the NON-SERVING CELL (and/or SCELL) and thefrequency (/time) synchronization according to the PCELL (and/or SERVINGCELL) is small).

FIG. 14 illustrates another situation in which the user device performsD2D operation.

Referring to FIG. 14, the user device may be required to perform a D2Doperation at the F2 frequency while having a specific cell serving as aserving cell (or PCELL) at F1 frequency. The user device may be locatedoutside the coverage of the NON-SERVING CELL (or SCELL) at the F2frequency. In this case, the NON-SERVING CELL (or SCELL) at the F2frequency may be referred to as an OUT-COVERAGE NON-SERVING CELL (orOUT-COVERAGE SCELL).

When it is assumed that the NON-SERVING CELL (and/or SCELL) performingthe D2D TX (/RX) operation is determined (or assumed) as OUT-COVERAGE,and the PCELL (and/or SERVING CELL) is IN-COVERAGE, the UE may applyfrequency synchronization and/or time synchronization related to the D2DTX (/RX) operation in the corresponding NON-SERVING CELL (and/or SCELL)according to some or all of the following rules.

It is assumed that the SERVING CELL (and/or PCELL) and the NON-SERVINGCELL (and/or SCELL) use (or belong to) different CARRIERs. Some or allof the following rules may apply only to a case when CARRIER associatedwith NON-SERVING CELL (and/or SCELL) and CARRIER associated with SERVINGCELL (and/or PCELL) have INTER-BAND (and/or INTRA-BAND CONTIGUOUS and/orINTRA-CONTIGUOUS) relationship.

(Rule#B-1) A rule may be defined to apply frequency synchronizationrelated to D2D TX(/RX) operation on the corresponding NON-SERVING CELL(and/or SCELL)) based on the IN-COVERAGE PCELL (and/or SERVING CELL).Here, as another example, a rule may be defined to apply timesynchronization related to D2D TX(/RX) operation on the correspondingNON-SERVING CELL (and/or SCELL)) based on the IN-COVERAGE PCELL (and/orSERVING CELL). Here, in another example, if the corresponding D2D TX(/RX) UE has an OUT-COVERAGE UE on the OUT-COVERAGE NON-SERVING CELL asa SYNCHRONIZATION REFERENCE, a rule may be defined to apply frequencysynchronization and time synchronization related to D2D TX (/RX)operation on the corresponding NON-SERVING CELL based on theOUT-COVERAGE UE (SLSS thereof). In an alternative, a rule may be definedto apply one of frequency synchronization and time synchronizationrelated to D2D TX (/RX) operation on the corresponding NON-SERVING CELLbased on the OUT-COVERAGE UE (SLSS thereof), and to apply the other offrequency synchronization and time synchronization related to D2D TX(/RX) operation on the corresponding NON-SERVING CELL based on theIN-COVERAGE PCELL (and/or SERVING CELL). Here, as another example, ifthe corresponding D2D TX (/RX) UE does not have an OUT-COVERAGE UE onthe OUT-COVERAGE NON-SERVING CELL as a SYNCHRONIZATION REFERENCE (i.e.,the D2D TX (/RX) UE itself is an independent SYNCHRONIZATION REFERENCE),frequency synchronization (and/or time synchronization) related to D2DTX (/RX) operation on the corresponding non-serving cell may beapplied/assumed based on IN-COVERAGE PCELL. In an alternative, D2D TX(/RX) UE itself configures (applies) one of time synchronization andfrequency synchronization) related to D2D TX (/RX) operation, and theother of D2D TX/RX operation related frequency synchronization and timesynchronization) may be applied/assumed based on IN-COVERAGE PCELL.

The proposed schemes described above may be implemented independently,but may be implemented in the form of a combination of some of theproposed schemes. The above-described proposed schemes may be definedsuch that they are limitedly applied only to the FDD system (and/or TDDsystem) environment. The proposed schemes described above may be definedsuch that they are limited to MODE 2 COMMUNICATION and/or TYPE 1DISCOVERY (and/or MODE 1 COMMUNICATION and/or TYPE 2 DISCOVERY). Inaddition, the above-described proposed schemes may be defined to belimited to the IN-COVERAGE D2D UE (and/or OUT-COVERAGE D2D UE) (and/orRRC_CONNECTED D2D UE (and/or RRC_IDLE D2D UE)). The proposed schemesdescribed above may be defined to be limited to only the D2D UE thatperforms only the D2D DISCOVERY (transmission/reception) (and/or the D2DUE performing only the D2D COMMUNICATION (transmission/reception)). Theproposed schemes described above may be defined to be limited to only asituation where only D2D DISCOVERY is supported (set) (and/or only D2DCOMMUNICATION is supported or set). The proposed schemes described abovemay be defined to be limited only to a situation where the D2D DISCOVERYSIGNAL reception operation is performed using in the other (UL) CARRIERhaving the INTER-FREQUENCY (and/or a situation where the D2D DISCOVERYSIGNAL reception operation is performed using the other INTER-PLMN-based(UL) CARRIER). The proposed schemes described above may be defined to belimited to the OUTB AND D2D RELAY operation (and/or the INBAND D2D RELAYoperation). The above-described proposed schemes may be defined to belimited to a situation where DRUE#N transmits D2D DISCOVERY-related(and/or COMMUNICATION related) SSS, and/or PSBCH (related to RELAYcommunication) using the CARRIER#Y. In addition, the proposed schemesdescribed above may also be applied to a situation where a D2D UEperforming a general D2D communication (not a D2D RELAY operation)transmits D2D DISCOVERY-related (and/or D2D COMMUNICATION related) SSSand/or PSBCH (and/or PSCCH and/or PSSCH and/or PSDCH transmission) usingthe CARRIER#Y. Also, the above-described proposed schemes may be definedto be limited to a situation where the D2D operation is performed usinga non-primary carrier rather than a primary carrier. In addition, theabove-described proposed schemes may be defined to be limited to asituation where there is no active serving cell using the carrier onwhich the D2D operation is performed (or when there is no cell to bedetected).

FIG. 15 is a block diagram illustrating the user device in which anembodiment of the present invention is implemented.

Referring to FIG. 15, the user device 1100 includes a processor 1110, amemory 1120, and a radio frequency unit 1130. Processor 1110 implementsthe proposed functionality, process and/or method as set forth herein.For example, the processor 1110 may receive measurement carrier(MEA_CARRIER) indication information indicating one downlink carrierused for downlink measurement and synchronization for D2D operation, andmay use one downlink carrier indicated by the measurement carrier(MEA_CARRIER) indication information to perform downlink measurement andsynchronization for the D2D operation.

The RF unit 1130 is connected to the processor 1110 to transmit andreceive radio signals.

The processor may comprise an application-specific integrated circuit(ASIC), other chipset, logic circuitry and/or data processing device.The memory may include read-only memory (ROM), random access memory(RAM), flash memory, memory cards, storage media, and/or other storagedevices. The RF unit may include a baseband circuit for processing theradio signal. When the embodiment is implemented in software, theabove-described techniques may be implemented with modules (processes,functions, and so on) that perform the functions described above. Themodule may be stored in the memory and may be executed by the processor.The memory may be internal or external to the processor, and may becoupled to the processor by various well known means.

What is claimed is:
 1. A method for transmitting a device-to-device(D2D) signal by a user equipment in a wireless communication system, themethod comprising: receiving a measurement carrier (MEA_CARRIER)indication information indicating one downlink carrier used for downlinkmeasurement and synchronization for D2D operation; and using onedownlink carrier indicated by the measurement carrier (MEA_CARRIER)indication information to perform downlink measurement andsynchronization for the D2D operation.
 2. The method of claim 1, whereinthe D2D operation is a transmission of a D2D discovery signal.
 3. Themethod of claim 2, wherein the D2D discovery signal is transmitted via anon-primary carrier rather than a primary carrier.
 4. The method ofclaim 2, wherein if there is an active serving cell for the userequipment, the serving cell using a non-primary carrier rather than aprimary carrier for transmission of the D2D discovery signal, theactivated serving cell is used to perform downlink measurement andsynchronization for the D2D operation.
 5. The method of claim 4, whereinif there is not an active serving cell for the user device, the servingcell using a non-primary carrier rather than a primary carrier fortransmission of the D2D discovery signal, the one downlink carrierindicated by the measurement carrier (MEA_CARRIER) indicationinformation is used to perform downlink measurement and synchronizationfor the D2D operation.
 6. The method of claim 5, wherein the onedownlink carrier is a carrier linked to the non-primary carrier ratherthan the primary carrier via system information.
 7. The method of claim5, wherein the one downlink carrier is a carrier not linked to thenon-primary carrier rather than the primary carrier via systeminformation.
 8. A user equipment comprising: an RF (Radio Frequency)unit for transmitting and receiving a radio signal; and a processorcoupled to the RF unit, wherein the processor is configured to: receivea measurement carrier (MEA_CARRIER) indication information indicatingone downlink carrier used for downlink measurement and synchronizationfor D2D operation; and use the one downlink carrier indicated by themeasurement carrier (MEA_CARRIER) indication information to performdownlink measurement and synchronization for the D2D operation.
 9. Theuser equipment of claim 8, wherein the D2D operation is a transmissionof a D2D discovery signal.
 10. The user equipment of claim 9, whereinthe D2D discovery signal is transmitted via a non-primary carrier ratherthan a primary carrier.
 11. The user equipment of claim 9, wherein ifthere is an active serving cell for the user equipment, the serving cellusing a non-primary carrier rather than a primary carrier fortransmission of the D2D discovery signal, the activated serving cell isused to perform downlink measurement and synchronization for the D2Doperation.
 12. The user equipment of claim 11, wherein if there is notan active serving cell for the user device, the serving cell using anon-primary carrier rather than a primary carrier for transmission ofthe D2D discovery signal, the one downlink carrier indicated by themeasurement carrier (MEA_CARRIER) indication information is used toperform downlink measurement and synchronization for the D2D operation.13. The user equipment of claim 12, wherein the one downlink carrier isa carrier linked to the non-primary carrier rather than the primarycarrier via system information.
 14. The user equipment of claim 12,wherein the one downlink carrier is a carrier not linked to thenon-primary carrier rather than the primary carrier via systeminformation.